Imaging devices configured to operate at cryogenic temperatures in a high-vacuum environment are highly sensitive to temperature variations. Some imaging devices have variably positioned shutters configured to establish different sized apertures, whereby the shutter is mechanically configured to have two or more apertures to support different fields of view and wavelengths. During the mechanical configuration, the shutter increases in temperature due to friction and heat transferred from a drive mechanism. In order for a high definition IR sensor to work correctly, the temperature of the shutter cannot rise more than 10 Kelvin during actuation. Failure to provide shutter thermal stability degrades the imaging performance. For instance, when the temperature of the shutter rises more than 10K, the wait period before the imaging device can be effectively used increases as the shutter temperature variation increases. It is not uncommon for prior art imaging devices to have a wait period that exceeds 10 minutes after shutter configuration.
Prior art devices having an interleaved iris design have multiple blades, such as four blades, that are forced together to transfer heat. These interleaved blades are typically ceramic coated, and thus are poor thermal conductors. As a result, the shutter experiences a large change in temperature during each change in position, and significant wait times are incurred while the shutter temperature stabilizes.
There is desired a shutter having a thermally stable variable aperture that provides continuous stable cryogenic temperature performance both at rest and while transitioning between aperture opening settings and is operable in a high vacuum environment. The aperture should maintain at least a 200K temperature differential from the “warm” parts including the drive mechanism, and not vary more than 10K during a transition.